Wind power is becoming an increasingly accepted source of energy in the world. In part, this reflects the opportunity to convert the kinetic energy of blowing wind that is plentiful offshore and in some land-based regions into mechanical power via a wind turbine to a generator that produces electricity. In part, the demand for wind power is enhanced by government subsidies and regulations that favor a renewable energy source like wind that does not collaterally produce greenhouse gases or acid rain over conventional fossil fuels like coal, natural gas, and petroleum.
Indeed, in 2015 Denmark generated 40% of its electric power from wind with at least 83 other countries in the world contributing to their electric power grids via wind power. Wind power capacity expanded to 336 GW in 2014, representing approximately 4% of total worldwide electric power demand.
A windmill is a mill that converts the kinetic energy of the wind into mechanical rotational energy by means of vanes. Centuries ago, these vanes resembled sails that rotated in the wind and were operatively connected to millstones for grinding grain or pumps for drawing water. Modem windmills tend to comprise wind turbines with rotating metal blades used to generate electricity or pump water for land drainage or groundwater extraction.
Horizontal axis wind turbines (“HAWT”) feature a tower with a fan-like rotor mounted at its top for rotation about a horizontal axis. Thus, the blades are rotated in a vertical plane by the wind. The rotor of a HAWT must face either into or away from the direction of the incoming wind, so a yaw mechanism is required to rotate the rotor about the vertical axis of the tower to maintain the rotor and its blades in proper alignment with the incoming wind flow. Since wind direction can frequently shift, the need for rotor redirection can be constant.
HAWT's are useful for capturing wind flows high above the ground level. Therefore, the towers are frequently very tall with blades that can exceed 330 feet in length. But, this tower must be structurally strong and robust to bear the weight of this rotor assembly, and resist oscillations caused by pressure pulsations produced by the blades interacting with the wind flow. Hence, while HAWT's are popular for production of wind power, they can be expensive to manufacture, install, and operate.
Vertical axis wind turbines (“VAWT”), by contrast, generally comprise a vertical shaft supporting a rotor assembly with blades that are rotated within a horizontal plane about a vertical axis by the incoming wind flow. The blades scoop up the horizontally flowing wind, which generally needs to be redirected to a more vertical flow to interact with the blades. Because the blades of such a rotor assembly turning about a vertical axis do not need to be specially aligned with the wind direction, there is no need for a yaw orientation mechanism and its associated power requirement. Thus, VAWT's are beneficial in locations where wind direction frequently shifts. They can be installed not only upon towers, but also upon the top of buildings and other structures. They can also interact with wind flows closer to the ground that are funneled by mesas, hill tops, and ridgelines. Finally, VAWT's generally have lower wind startup speed requirements compared with HAWT's with VAWT's being able to commence electricity production using wind flows at speeds as low as six miles per hour.
U.S. Pat. No. 335,388 issued to Serdinko in 1886 shows an early example of a HAWT. The blades rotate within a circular frame about a horizontal axis. A hemispheric domed roof protects the upper half of the blades from the incoming wind. A weather vane mounted to the top of the dome interacts with the incoming wind to turn the circular frame of the blade assembly in proper alignment with the wind without redirecting the wind flow within the turbine. A wing separately mounted to the dome detects overly strong winds to cause the blades to turn via some associated gears with their edges directed into the wind and stop rotating. A suspended weight reverses this process to reorient the blades with respect to the wind once it decreases to a safe speed.
By contrast, U.S. Pat. No. 1,100,332 issued to Smith in 1914 shows an early example of a VAWT. A rotor assembly having two sets of vanes positioned in a vertical plane is rotated about a vertical shaft by the incoming wind. The lower set is contained inside the rotor assembly. The upper set of vanes having a peculiar surface shape are secured at their bottom edges to the top of the rotor assembly, and at their top edges to a ring through which the rotor shaft extends. The blowing wind engages these top vanes to start the rotor assembly turning about the shaft where the wind interacts with the vanes mounted inside the rotor assembly to provide greater force to turn the rotor. But both sets of vanes merely catch the incoming wind flow without redirecting it inside the rotor assembly.
U.S. Pat. No. 1,592,417 issued to Burke discloses another VAWT in which spiral blades rotate around a vertical shaft to form a wind wheel assembly. The blades gradually decrease in width toward their lower ends to form a substantially frusto-conical shaped wheel. The frusto-conical shape of this resulting wind wheel tends to catch the incoming wind. Arcuate wings mounted to the periphery of the wind wheel provide surface area to direct the incoming wind into the openings of the wind wheel. However, the blades do not scoop or redirect the wind flow inside the wind wheel. Indeed, it appears from the drawings of the Burke patent that the rotating blades might cause the incoming wind flow to boomerang back upon itself. Thus, the arcuate wings are probably meant to overcome this turbulent air flow created by the rotating blades.
U.S. Pat. No. 372,148 issued to Henderson provides another early example of a VAWT windmill. The wind wheel containing a series of concave-shaped vanes is mounted about a vertical axis inside a rounded cone having only one side covered, so that the incoming wind flow is only permitted to bear against the vanes of one side of the wind wheel. This air flow bears against the concave surfaces of the vanes to rotate the wind wheel without being redirected inside the cone. Again, it appears that the wind flow may be turned back upon itself, which would cause turbulence.
U.S. Pat. No. 7,040,859 issued to Kane discloses a more recent example of a wind turbine. A series of vanes mounted to the bottom of a solid-topped cone comprises the turbine rotor. They revolve around a vertical axis as the incoming wind flow catches the surfaces of the vanes and then exits in a horizontal plane through the opposite side of the rotor. No updraft of the wind flow is created for the solid cone top prevents vertical outflow of the wind.
An alternative design for a VAWT is exemplified by U.S. Pat. No. 4,508,973 issued to Payne. The wind turbine comprises a housing with side inlets defined by a series of radial stationary vanes that join a conical, upwardly ramped floor to define passageways for the incoming wind flow. The conical floor surface creates an updraft for the wind flow as it travels through the passageways. The upwardly directed wind flows pulse against a propeller mounted to a vertical axis above the passageways. The wind flow exits through the top of the housing. The rotating propeller is operatively connected to a generator for producing electricity. See also U.S. Pat. No. 1,519,447 issued to Fortier-Beaulieu.
U.S. Pat. No. 4,018,543 issued to Carson et al. discloses a whirlwind power system in which a series of spirally-shaped stationary vane walls are mounted radially to the sides of a conical earthen mound. Like Payne and Fontier-Beaulieu, the incoming wind flows through the passageways directed upwardly by the ramped earth. The spiral vane walls create turbulence for the air flow to more actively turn a propeller mounted in the upper region of the structure on a vertical axis. U.S. Pat. No. 4,017,205 issued to Bolie adds a dome above the conical structure. The dome enhances the updraft of the airflow caused by the conical structure. See also U.S. Pat. No. 8,128,337 issued to Pezaris.
Other VAWT devices dependent upon an air updraft locate the propeller within the bottom portion of the device. For example, U.S. Pat. No. 4,070,131 issued to Yen shows a tornado-type wind turbine featuring a tower the walls of which comprise a series of movable vanes. Wind flows into the tower through openings in the side between the vanes. The vanes interact with the wind to create a vortex flow that moves in an upwards direction. The resulting updraft inside the tower draws wind through the bottom of the tower to rotate a propeller mounted on a vertical axis in the bottom portion of the tower.
U.S. Pat. No. 8,961,103 issued to Wolff discloses an omni-directional vertical axis wind turbine that can be mounted to the roof of a building. This is a large, complicated structure comprising a collector assembly with a series of inlet passages for collecting the incoming horizontal wind flow. The passages are defined by a series of stationary walls. The incoming air flows interact with a series of angled vertical panel members contained inside the collector assembly to redirect the air flow. These redirected air flows then interact with the incoming air flows to create a swirling stream of air flow inside the collector assembly. A stator assembly having a series of stationary angled vanes is mounted to the bottom of the collector assembly. Below the stator assembly is a turbine rotor mounted to a vertical axis. The swirling stream of airflow inside the collector assembly is directed downwardly by the vanes of the stator assembly to rotate the turbine rotor as the air flow exits the bottom of the structure.
Still other VAWT devices use horizontal airflow to turn a turbine rotor mounted to a vertical axis without vertical lift. Helically-shaped turbine blades are necessary for catching the airflow to turn the blades around the vertical axis. The air flow exits the opposite side of the structure. See U.S. Pat. No. 8,360,713 issued to Carosi et al., and U.S. Published Application 2012/10183407 filed by Vallejo. Carosi requires two turbine rotors having helically-shaped blades rotating in opposite directions about the vertical axis. U.S. Pat. No. 9,482,204 issued to Plourde et al. shows a wind turbine comprising three different sets of turbine rotors. The turbine blades rotating about the vertical axis feature flat vertical walls ending in a curved hook, thereby creating a high draft side and a low drag side along opposite sides of the blade to improve the horizontal airflows that bear against the turbine blades to rotate the rotors.
However, these VAWT's in the prior art have complicated structures with many moving parts. This necessarily increases the capital costs and operating costs for the VAWT. It would be beneficial to provide a vertical axis wind turbine of simpler design that can use the blades of the turbine rotor, itself, to redirect horizontal incoming air flow into vertical air flow that exits the turbine at or near the top, bearing against the blades of the turbine in the process to rotate the turbine about a vertical axis to produce electricity via an associated generator. There should be no need for separate turbine propellers or ramped surfaces inside the rotor separate from the turbine blades for creating vertical lift. By having the blades of the turbine rotor do all the work for redirecting the incoming air flow to create vertical air flow, the number of parts for the wind turbine can be significantly reduced.